1. Field of the Invention
The present invention relates generally to an apparatus and method for generating hydrogen and oxygen. The invention relates more specifically to an apparatus and method for the solar-augmented electrolytic and thermal production of hydrogen and oxygen, with the hydrogen either exported from the system as a product, or retained as fuel for an electrolytic fuel cell. The invention thus further relates to an integrated, continuously- or intermittently-operable system providing both hydrogen and oxygen generation and utility load leveling capabilities.
2. Description of the Related Art
Hydrogen, a clean burning fuel and raw material for the manufacture of numerous products, is conventionally produced from limited and non-renewable fossil fuels, or from water. Though water is abundant and renewable, it is a very stable compound because of the strength of the hydrogen - oxygen bond. Accordingly, using water as the feedstock to produce hydrogen requires a substantial energy input.
Past well-known methods of producing hydrogen from water involve the electrolysis of a potassium, or sodium hydroxide, or sulfuric acid electrolyte. Most recently the use of Solid Polymer Electrolytes (SPE) and Proton Exchange Membranes (PEM) has allowed the direct electrolysis of water. All of these processes require the input of substantial electrical energy and a demineralized water feedstream.
Another well-known electrolytic process, utilized much more frequently than water electrolysis, is the industrial electrolysis of aqueous alkaline chlorides to produce chlorine and caustic soda. Also, in the chlorination of organic compounds, much of the chlorine is retained in the form of hydrogen chloride or hydrochloric acid. The recovery of the chlorine from aqueous and gaseous hydrogen chloride is of great importance to the chloralkaline industry; this is commonly achieved either electrolytically or thermally.
Thermal recovery of chlorine from hydroge chloride is conventionally accomplished by the "Deacon Process." In this process hydrogen chloride is oxidized with oxygen, typically at 400.degree.-450.degree. C., producing chlorine and water. U.S. Pat. No. 4,799,357 describes a method and apparatus for dissociating hydrogen chloride by using solar, thermal, and photolytic energy with copper or silver as a reagent. Solar recovery of chlorine from hydrochloric acid has also been suggested by H. B. Gray, Science, Vol. 214 (1981), 1201, using the transition metal complex ion, hexachloroiridiate (IV). The crystal field and electron transfer spectra of Group VIII transition metal complexes has been described by C. K. Jorgensen, Acta Chimica Scandanavica, Vol. 10, No. 4 (1956), 500, 518; Vol. 11, No 1 (1957), 151, 166.
The solar conversion of water and chlorine into hydrochloric acid and oxygen has been investigated by numerous researchers over a two hundred year period, as described by J. W. Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, (1956). The reaction is both slow and inefficient, however, and has not been applied to practical use. The reaction of steam and chlorine to produce hydrochloric acid and oxygen has been well known, as documented by E. R. Riegel, Industrial Chemistry, Fifth Ed., (1949).
The electrolysis of hydrochloric acid to produce hydrogen and chlorine is described in U.S. Pat. No. 4,239,607, which discloses a method and apparatus using carbon slurry electrodes to increase the electrode surface area, and therefore attempt to lower the cell overvoltage.
The electrolysis of hydrochloric acid into hydrogen and chlorine and their subsequent recombination has been investigated by the U.S. Department of Energy, "Hydrogen/Halogen Energy Storage System, Final Report," Brookhaven National Laboratories, February 1979. The report describes a proposed utility load leveling battery using regenerative hydrogen chlorine cells. The proposed battery would have been cyclically charged as an electrolysis cell producing hydrogen and chlorine with off-peak electrical power, and discharged as a hydrogen/chlorine fuel cell to produce peaking power and thereby provide load leveling.